Proton radiotherapy as a treatment strategy to increase survival in locally advanced pancreatic cancer in the body and tail: a retrospective study

BACKGROUND: Long-term outcomes and prognostic factors of proton radiotherapy for locally advanced pancreatic cancer (LAPC) in the body and tail are still unknown. The aim of this study was to determine the prognostic factors after proton radiotherapy in a large group of patients with LAPC in the body and tail. METHODS: The medical records of 200 patients with LAPC in the body and tail who underwent proton radiotherapy between February 2009 and January 2021 at the Hyogo Ion Beam Medical Center were retrospectively reviewed to identify prognostic factors that contribute to long-term survival. RESULTS: The overall survival rate at 1- and 2-year after PT was 69.6% and 35.4% with a median overall survival of 18.4 months. The 1- and 2-year local progression-free, and progression-free survival rates were 84.3% and 68.0%, and 44.3% and 19.4%, respectively. In multivariate analysis, superior mesenteric artery (SMA) invasion (SMA only invasion vs. celiac artery only invasion; P = 0.049: SMA and celiac artery invasion vs. celiac artery only invasion; P = 0.017), carbohydrate antigen 19-9 (CA 19-9) level ≥ 231.9 U/mL (P = 0.001), anterior peripancreatic invasion (P = 0.006), and incomplete scheduled concurrent chemotherapy (P = 0.009) were statistically significant prognostic factors for overall survival. There was no significant difference in local progression-free survival; however, distant metastasis-free survival was statistically worse in patients with prognostic factors than in those without. CONCLUSIONS: Proton radiotherapy for LAPC in the body and tail may be a valuable multidisciplinary treatment option. Patients with SMA invasion, higher pre-proton radiotherapy serum CA 19-9 level, anterior peripancreatic invasion, or incomplete scheduled concurrent chemotherapy had worse overall survival because of worse distant metastasis-free survival, suggesting that distant metastases have a significant impact on overall survival in such patients. Trial registration: Retrospectively registered.